1. Field of the Invention
The present invention relates to an image forming apparatus such as an electrophotographic copying apparatus, and more particularly to an image forming apparatus having a linear array of a plurality of photosensitive members and utilizing such photosensitive members in an independent manner, thereby forming cyan, magenta, yellow and black images respectively corresponding to the photosensitive members and synthesizing these images to form a color image.
2. Related Background Art
There is already known a laser beam image forming apparatus, in which laser light sources are provided as image exposure means respectively corresponding to four electrophotographic photosensitive members arranged in a linear array and are controlled respectively corresponding to the image information of cyan, magenta, yellow and black colors to form electrostatic latent images respectively corresponding to the cyan, magenta, yellow and black colors on the four electrophotographic photosensitive members, then such electrostatic latent images are respectively developed and the developed images are synthesized to obtain a color image.
Also there is known an LED light image forming apparatus in which four LED's are provided respectively corresponding to the photosensitive members, as the light sources for forming the electrostatic latent images of cyan, magenta, yellow and black colors, in place for the laser beam sources in the above-mentioned image forming apparatus.
In the aforementioned laser beam image forming apparatus, in order to synthesize the images of cyan, magenta, yellow and black colors in mutually registered manner, it is required to exactly match the scanning operations of the four laser light sources, provided respectively on the four photosensitive members, securely in the main and subscanning directions, but in practice it is difficult to exactly match the four laser lights in the main and subscanning directions.
On the other hand, in the above-mentioned LED light image forming apparatus, it is relatively easy to meet the above-described requirements of matching in the main and subscanning directions, but such apparatus is even more expensive since a plurality of expensive LED chips have to be jointed in a linear array to obtain a jointed LED element. Besides, since the LED chips fluctuate in the light emission characteristics, the image reproducibility is deteriorated in the main scanning exposure direction, relative to the movement of the photosensitive member, to be exposed by the above-described jointed LED element, because the exposure condition differs for each LED chip.
Also in the electrophotographic copying apparatus capable of forming a color image, the above-described jointed LED element has to be provided for each of the plurality of photosensitive members, and the light emission characteristics become different among the plurality of jointed LED elements corresponding to the plurality of photosensitive members. Consequently, there emerges a difficult requirement of matching the light emission characteristics among such jointed LED elements.